Constant-potential submerged-melt metal-arc welding



Dec. 5, 1950 H. E. KENNEDY 2,532,411

CONSTANT-POTENTIAL SUBMERGED-MELT METAL-ARC WELDING Filed Oct. 29, 1949 3-PHASE JZ A.C.

INVENTOR HARRY E. KENNEDY ATTORNEY Patented Dec. 5, 1950 CONSTANT-POTENTIAL SUBMERGED-MELT luETAL-ARC WELDING Harry E Kennedy, Berkeley, Calif assignor to The Linde Air Products Company, a corporation of Ohio Application October 29, 1949, Serial No. 124,400

1 4 Claims.

This invention relates to electric welding, and more particularly to submerged-melt metal-arc welding in which a metal electrode is'fed toward the work through a layer of granular flux which is non-conductive when cold but is conductive and fuses during the welding operation.

The resistance of an arc decreases as the current increases. This is so because the degree of ionization 7 increases with increased current. Therefore, the IR drop in the are decreases as the current increases. This results in instability of the arc unless compensatory means are included in the circuit. In order to render an are stable it is customary to include an element in the circuit with a characteristic opposite to the arc, such as a suitable resistor, or an inductance, or a specially designed generator.

Electric welding generators are usually constructed so as to have a relatively high open circuit voltage which decreases when current is being drawn. Such current is predetermined b the characteristics of the circuit; the welding voltage, b the length of the arc.

In automatic metal-arc welding a continuous electrode is fed to the welding zone at an automatically variable rate so as to maintain the voltage across the arc at a, predetermined substantially constant value. In the past, submerged rnetal-arc welding circuits were designed to supply current to the arc with a decidedly drooping voltage characteristic, the open circuit voltage being considerabl higher than the welding voltage, and the voltage applied to the are falling rapidly with any increase in welding current. This was intended to stabilize the welding operation, but in order to obtain satisfactory welding, the arc-voltage was maintained substantially constant by automatically changing the rate of rod-feed. The necessary equipment for this purpose was expensive to bu and to keep in good working order. Also, stabilizing resistors used up a considerable amount of power, but stable metal-arc welding with a coated electrode orwith a bare electrode in air was impossible without at least a series-resistor or reactance for this purpose in the welding cireasy and great uniformity of welding results. In order to do this a device for continuously feeding the metal electrode at a preselected rate is used. The power source is a constant-potential generator having a current supplying capacity of the order of 19,000-81,000 amperes per square inch of welding rod cross-section. Direct current is preferred. The particular type of machine is of little consequence. A flatcompound machine is entirely suitable, or a voltage regulator may be connected to an ordinary welding generator so as to maintain a constant voltage. The need for any current limiting device under these conditions is eliminated and the generator is separately excited. It should be emphasized that unlike prior welding systems, in the present invention the open circuit voltage is substantially equal to the weldingvoltage. Electrocutions have resulted by accidental contact with electrical welding equipment, especially in damp locations. In the present system such accidents are most unlikely, because of the greatly reduced open circuit voltage (25-45 volts).

The rate at which the welding rod is fed to the welding zone determines the current, which may be adjusted by adjusting the speed of the rod to any desired value within the capacity of the machine. The welding voltage may be adjusted to any desired value without altering the current. This combination is found to be ver eifective in mechanized submerged arc welding. As in ordinary welding, the electrode size should be chosen for the range of current to be used. A current density of the order of 19,000-81,000 amperes per square inch of rod cross-section is entirely satisfactory.

The present method of automatic submerged melt welding makes possible a much higher current output from a given sized generator. Fewer armature conductors are required because of the lower open circuit voltage. Therefore, their cross-section can be correspondingly increased. The welding machine need not have a current controlling device and the rod-feed mechanism need have no automatic control.

In the drawing the single figure is a diagrammatic View, partly in elevation, of a submerged melt metal-arc welding system illustrating the invention.

As shown in the drawing a welding rod or wire In is fed at a substantially constant.v rate from a reel l2 by a drive wheel M which is driven by a rod feed motor IS. The speed of the motor I6 can be set as desired by adjustment sible, welding flux. The flux is supplied to the welding zone 30 from a hopper "32"tl11'0ugh a hose 33. The hopper 32 is carried bya-support 34 which also is mounted on the carriage mounting the head support 2 1.

The work W is connected to a constant po-" tential welding current source 3B by a lead. such as an insulated conductor 48 having 'as' little resistance as possible. Similarly, the -.-welding head 22 is connected to the source 38 by a lead such as an insulated conductor 42 f low resist- While any source of constant potential welding current can be used, a fiat-compound generator M has proved to be highly satisfactory. The generator '6 comprises an armature it which is driven by a constant speed A. 'Q-motor The motor 38 is connected to a suitable power line althrough a switch 52. Theshunt field winding 54 of the generator is energized suitable source of direct current, DC, 30

y a through a rheostat 56. The interpole windings 58 and the series .field winding es of the -generator are connected in series with the output circuitiiZ which includes the low-resistance conductors 16 and 52, the rod and the work W.

The generator at is designed so that the voltage-current output characteristic curve thereof is substantially flat, i. e. does not vary more than :3 volts between no-load and full load current valuesyth'eiull load voltage beingsubstantially equal to the open circuit voltage. "No

stabilizing resistance or reactance is used in the welding current circuit, the arc-voltage being about equal to the generator voltage and being kept as constant aspossible during the operation of the system.

The stability of the welding operation is made possible by the vapor mantle formed. in the'fused fluxabout the arc. Numerous welds were made according to the invention on 12 and l4 gauge steel with excellent results. With and rods of steel carrying 250 amperes, i. e., at current densities of 81,000 and 36,000 amperes per square inch of rod cross-section, respectively; and fed at 100 inches per minute continuous beads were obtained. There was none of the skipping present which is usually experienced with the prior standard type voltage control. Each head was A;" wide and approximately high. Probably the most-noticeable featurewas that in welding 12 and lO-gauge steel with small diameter "rod, the fused material at the root of the weld did not show the usual cold "casting experienced with the old type of welding where the voltage regulated the rod feed. Instead, Instead, there seems to be a beneficial wetting action. v

The welding action is similar to that disclosed in Patent 2,043,960 to Jones, Kennedy and Rotermond, except that no automatic voltage control device is necessary. Nor is any rod feed control necessary, therod being fed at any desired 'constantspeed'by'the motor It.

'The granular flux blanket has the remarkable effect, in the current densit rangeof19,'000

81,000 amperes per square inch of rod crosssection, of stabilizing the welding operation,

making it unnecessary to use any resistance or reactance in the welding circuit for this pur- 5 pose. This greatly simplifies the system. Complicated and expensive rod-feed controls are "eliminated, therod being fed to the welding zone at a constant rate by a simple motor,the speed of which can be adjusted manuall as desired.

I claim:

1. "A constant :potential metal-arc welding =system"comprising a constant potential source of welding current-having a current supplying -capacitybf-theorder of 19,00081,000 amperes per square-inch fof welding rod cross-section, means for feeding a bare welding rod composed "ofmetal at a constant rate toward a welding zonezon work composed of metal, leads connecting said source of welding current directly to the work and to the weldingroi-so. thattwelding current flows throughsuch rod and thework rat a current densityo'f' the order of 19,000-8L000 amperes per square inch of welding rod cross sectioniorming awlding arc whichjuses the end of the rodand-the.adjacentmetal of the work, and means supplying a granular 'iiux medium to suchv welding zone which in such current. density rgngestabilizes the welding arc, whereby fora rod ofagiven-size the amount of welding current inherently-depends .upon the speed at which such rodis fed towardth-e-welding zone, and the resulting welding operation issostable-lthat theuneed forrod teedand voltage controls, as wellas stabilizing resistors and reactors in the weldingcircuit is eliminated.

-2. Processtof metal-arc welding which comprises connecting metal 'work to the --weldednto one side of aconstantpotential source of welding current having a current supplying capacity of the order.of.19,000-81,G00-'amperes -per square inch of welding rod cross-section, connecting a bare welding rod-composedof metalto the other side or said constant potential source of welding current, covering .the end of mid trod and the adjacent metal to bewelded withian inert granular flux mediumwhich-in suchcurrent density rangeeffectively-stabilizes thearc, feeding-said rodtoward-thework ata substantially constant rate, supplying welding-current '50 to such .rod at ia current density of the order of'19,000-81,000-amperes pers ua-r-e inch of welding .rod cross-section, and fusing the end of such rod and the adjacent work metal in the welding zone in accordance with the rateof feed of said welding rod, the effector such inert granular fiuxmedium insuch current density range being ato stabilize the welding-operation.

.3. Process of welding metal Work lll'idel .a blanket of inert .granular fusible which is "50 non-conductive when cold, which comprises connectinga bare weldingrodpf metalto one side of asource of welding current haringe, substan-r tially constant potential between no -load and full load currentvalues, said sourcel having a cur- 05 rent supplying capacity of the order of 19,000-

81,000 amperes per square inch. of welding wrod cross-section, connecting the work to the other si'de'of'saidsource of welding current, feeding a stream of inert granular'fusible flux on "the work in the zone 'to be welded, feeding welding rod through such flLlXl toward the "work at a substantially constant rate, "supplying weldingcurren't'to such'rod'ata current densit of the order "or 1'9,000 81-',000- amperes per square inch of welding "rod "cross section, fusing the end of the welding rod, the flux and the adjacent metal of the work under such flux, and moving the rod and granular flux stream over the work along a desired path, the amount of welding current supplied by said source being a direct function of the rate at which the rod is fed toward the welding zone, and the fused flux having the beneficial efiect in such current density range of stabilizing the welding operation.

4. A constant-potential submerged-melt metalarc welding process which comprises discharging a stream of inert granular fusible flux which is non-conductive when cold, on metal work to be welded along a desired path, applying a potential of between 25 and 45 volts of a welding current source across a bare metal welding rod and the work, feeding such rod at a substantially constant rate toward the work through such stream of flux, fusing the end of the rod and the flux and the adjacent work metal with welding current flowing through such rOd and the intervening flux and the work at a current density of the order of 19,000-81,000 amperes per square inch of welding rod cross-section, moving the rod along such path while maintaining the rod-feed at such rate, and maintaining the potential applied across the rod and the work to within :3 volts of the voltage applied thereto prior to starting the process, the welding arc being stabilized in such current density range by the vapor mantle which is formed thereabout in the fused flux.

HARRY E. KENNEDER REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,483,612 Morton Feb. 12, 1924 2,300,670 Hopkins Nov. 3', 1942 2,332,950 Tannheim Oct. 26, 1943 2,430,055 Kennedy Nov. 4, 1947 

